1. Field of the Invention
The present invention relates to woven fabrics, and more particularly to multi-ply woven fabrics of the type which may be provided with internal stiffening elements and rigidified such as by resin impregnation to provide a strong and yet lightweight structural panel.
2. History of the Prior Art
Woven multi-ply, three-dimensional fabrics of the type having opposite woven face plies and a plurality of intermediate woven ribs which extend between and are interwoven with the face plies are well known in the art. Such fabrics have proven capable of being reinforced such as by the insertion of stiffening elements into the open spaces therein and rigidified such as by resin impregnation to provide panels which are strong, yet lightweight and inexpensive. The uses for such panels are virtually unlimited, and presently include walls, roofs, floors, airframe components, and insulation.
Examples of multi-ply, three-dimensional woven fabric articles and the methods of making the same are provided by U.S. Pat. No. 3,090,406 of Koppelman et al, issued May 21, 1963. As described in Koppelman et al a multi-ply, three-dimensional fabric may be woven on a conventional shuttle loom so as to have opposite face plies and an intermediate rib ply which zig zags between and is interwoven with the opposite face plies.
The woven fabric disclosed in the Koppelman et al patent has proven to be highly useful in the manufacture of panels for a wide variety of applications. Upon weaving of such fabrics mandrels are typically inserted within the triangular-shaped spaces therein during resin impregnation and curing so as to rigidify the structure. Frequently the triangular-shaped spaces are filled with foam elements prefabricated to the size of the triangular-shaped openings and inserted thereinto using mandrels. Where foam inserts are used they may be placed in the fabric openings prior to resin impregnation so as to hold the fabric erect and rigid during impregnation. The resulting rigidized article comprises a panel which is lightweight, strong and yet relatively inexpensive. The foam inserts, where used, add considerable strength to the article as well as enhancing the insulating properties thereof.
However fabrics of the type described suffer from a number of limitations which may render them impractical or unsuitable for certain applications. One of the most serious limitations of such fabrics is their rather low compressive strength. While the foam inserts, where used, add somewhat to the resistance of the article to compressive forces, the compressive strength as well as other structural features of the article may prove inadequate for many applications. For example panels measuring approximately 3/4 inch in thickness and made of fiberglass yarns which have been resin impregnated and supported by foam fillers are typically capable of withstanding a maximum of 150 to 200 lbs. per square inch. Such articles furthermore lack the versatility which may be desired for certain applications. For example it may be highly desirable to be able to insert stiffening elements into the woven fabric so as to greatly rigidify the article between the opposite face plies. At the same time, however, it may be essential that the filler elements be thin so as to be light in weight or to conserve on materials, thereby making it impractical to fill the entire spaces within the woven fabric.